Gravity based brake stroke sensor methods and systems

ABSTRACT

Methods and systems for measuring a brake stroke of an air brake assembly utilize a sensor, such as an accelerometer, mountable on a movable component, such as a brake cam shaft, of the air brake assembly that is external of the brake chamber of the air brake assembly for detecting an acceleration of the movable component during a braking event. The sensor generates an output signal that depends on a magnitude of the detected acceleration, which is sent to a microcontroller coupled to the sensor. The microcontroller translates the sensor output signal to a value corresponding to a displacement of the movable component of the brake assembly during the braking event and calculates a brake stroke distance based on said value.

PRIORITY APPLICATION

This application claims priority to co-pending U.S. ProvisionalApplication No. 60/600,605, filed Aug. 11, 2004, entitled “GRAVITY BASEDBRAKE STROKE SENSOR”, which is incorporated herein by this reference.

FIELD OF THE INVENTION

The present invention relates generally to the field of air brakesystems, and more particularly to systems and methods for measuring thebrake stroke for heavy-duty trucks and other equipment that use airbrake systems utilizing, for example, an accelerometer and amicrocontroller or programmable logic device for the brake strokemeasurement

BACKGROUND OF THE INVENTION

Most air brake systems utilize a sealed housing or brake chamber, anexample of which is illustrated schematically in FIG. 1. Within thebrake chamber 10 is a diaphragm 12 attached to a push rod 14 thatextends through one side 16 of the brake chamber 10. The opposite sideof the diaphragm 12 creates an air cavity 18 within the brake chamber10. The air pressure in the cavity 18 rises when the brake pedal of thevehicle is depressed. The diaphragm 12 deforms, and the air pressurerises, in proportion to the amount of force applied to the brake pedal.The push rod 14 responds to such deformation by moving with thediaphragm 12 to cause engagement of the braking surfaces. When the airbrake system is properly adjusted, the push rod 14 travels a distance ofup to about two inches from a point at which the brake is completelyreleased to a point at which it is fully actuated. Over time, as thebrakes are repeatedly applied, the travel distance of the push rod 14increases, eventually requiring a readjustment of the brake systembefore the braking capability deteriorates to a level that renders thevehicle unsafe.

Typical electronic brake stroke sensors currently use magnetic orresistive means to measure the amount of push rod displacement during abraking event. These sensors and electronics are integrated into thebrake chamber causing the user to have to purchase and install an entirebrake chamber assembly equipped with the stroke sensing equipment. Theprior art is generally divided into two categories, namely mechanicalvisual indicators and electronics integral to the brake chamberassembly. The mechanical visual indicators are not capable of providingthe brake stroke information remotely. A person must also be present toobserve the brake stroke while another person operates the brake system.Unfavorable weather conditions may discourage visual inspection, whichrequires crawling under the truck for inspection of each brake strokeindicator. The brake chambers with integrated electronics are expensiveand therefore not good candidates for retrofit applications.Additionally, the installation is a much more complex process than wouldbe acceptable for a retrofit into existing equipment.

Accordingly, there is a present need for an electronic brake strokesensor capable of integration into an existing brake system without theneed for extensive redesign of the brake chamber. Moreover, there is apresent need for an electronic brake stroke sensor that requires nomoving parts and can be installed without regard to alignment andprovides for self-calibration, thus avoiding the problem of misalignmentor inaccurate readings.

SUMMARY OF THE INVENTION

It is a feature and advantage of the present invention to providemethods and systems for measuring a brake stroke of an air brakeassembly utilizing, for example, a sensor that has no moving parts tobreak or wear out.

It is a further feature and advantage of the present invention toprovide methods and systems for measuring a brake stroke of an air brakeassembly utilizing components that can be installed without alignmenttools or brackets in that the sensor automatically generates a zero orreference regardless of the installed position on the brake cam shaft.

It is an additional feature and advantage of the present invention toprovide methods and systems for measuring a brake stroke of an air brakeassembly using a sensor that is sealed and impervious to contaminants

It is another feature and advantage of the present invention to providemethods and systems for measuring a brake stroke of an air brakeassembly employing electronic components that output data that can bedigitized and transmitted elsewhere for data collection purposes.

To achieve the stated and other features, advantages and objects,embodiments of the present invention embodiments of the inventionpropose methods and systems for measuring the brake stroke of an airbrake assembly utilizing, for example, a sensor, such as anaccelerometer, that is mountable on a movable component, such as a brakecam shaft, of the air brake assembly external of the brake chamber ofthe air brake assembly for detecting an acceleration of the movablecomponent during a braking event and for generating an output signalthat depends on a magnitude of the detected acceleration. In addition,coupled to the sensor is a microcontroller on which is encoded programcode consisting at least in part of instructions for translating thesensor output signal to a value corresponding to a displacement of themovable component of the brake assembly during the braking event and forcalculating a brake stroke distance based on that value.

Preferably, in embodiments of the invention, the sensor is adapted fordetecting acceleration of the movable component along at least twodifferent axes relative to the movable component during the brakingevent. For such purpose, a dual axis accelerometer or at least twounidirectional accelerometers can be employed. In an embodiment of theinvention, the sensor output signal comprises a direct current voltagethat varies in proportion to the magnitude of the detected acceleration,which is translated by the microcontroller to angular valuesrepresenting a rotary displacement of the brake cam shaft during thebraking event. In a preferred embodiment, the movable component of theair brake assembly comprises a brake cam shaft of the air brakeassembly, but in other embodiments, the movable component comprises, forexample, a push rod of the air brake assembly or a cam roller of the airbrake assembly.

In an aspect of the invention, the microcontroller can be coupledwirelessly to the sensor, and a display device can also be coupled tothe microcontroller for presenting brake stroke distance-relatedinformation to a user, for example, at a remote terminal coupled to themicrocontroller. Further, the display device can be coupled wirelesslyto the microcontroller and can include, for example, a portablehand-held display device coupled wirelessly to the microcontroller.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome more apparent to those skilled in the art upon examination of thefollowing, or may be learned from practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram that illustrates an example of a brakechamber for an air brake system for embodiments of the invention;

FIG. 2 is a cut-away view of a brake drum and associated components foran air brake system for an embodiment of the invention;

FIG. 3 is a schematic diagram that illustrates an example of keycomponents and flow of information between key components forembodiments of the invention;

FIG. 4 is a flow chart that illustrates an example of the process ofmeasuring a brake stroke of an air brake assembly for an embodiment ofthe invention;

FIG. 5 is a schematic diagram that illustrates an example of orthogonalaxes of a dual axis accelerometer in the gravitational field of theearth for an embodiment of the invention;

FIG. 6 is an output voltage diagram that shows an example of the x-axisoutput voltage and corresponding y-axis output voltage in anacceleration event for an embodiment of the invention;

FIG. 7 is a schematic diagram that illustrates an example of initial andfinal positions of the slack adjuster and push rod in a braking eventfor an embodiment of the invention; and

FIG. 8 is a schematic diagram that illustrates an example of deploymentof a plurality of brake stroke sensors in a vehicle brake system for anembodiment of the invention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the invention,one or more examples of which are illustrated in the accompanyingdrawings. Each example is provided by way of explanation of theinvention, not as a limitation of the invention. It will be apparent tothose skilled in the art that various modifications and variations canbe made in the present invention without departing from the scope orspirit of the invention. For example, features illustrated or describedas part of one embodiment can be used on another embodiment to yield astill further embodiment. Thus, it is intended that the presentinvention cover such modifications and variations that come within thescope of the invention.

Referring to FIG. 1, as previously noted, the brake chamber 10 of theair brake system converts air pressure to mechanical pressure when airpressure enters the cavity 18 and pushes on the diaphragm 12, which inturn pushes on plate 22 and push rod 14. FIG. 2 is a cut-away view of abrake drum 20 and associated components for an air brake system for anembodiment of the invention. Referring to FIG. 2, the push rod 14connects to a lever referred to as a slack adjuster 24. The slackadjuster 24 is in turn connected to a rotating shaft 26. An adjustingscrew or nut 28 in the slack adjuster 24 is used to set its position onthe on the shaft 26 to adjust the brakes. When the brakes are applied,the push rod 14 pushes on the slack adjuster 24 causing it to rotate theshaft 26 and a cam or S-cam 30 between two brake shoes 32. The rotatingS-cam 30 pushes on rollers or pads 34 connected to the brake shoes 32,which causes the brake shoes 32 to rub against the brake drum 20 to stopthe vehicle. While an air brake using an S-cam is illustrated in theexample depicted in FIG. 2, embodiments of the present invention can beutilized in other types of air brakes, such as wedge brakes and/or discbrakes.

In an aspect of the present invention, a system and method is providedfor measuring the brake stroke, i.e., the push rod travel distance, forheavy-duty trucks and other equipment that use air brake systems. In anembodiment of the invention, the brake stroke measurement is made usingan accelerometer and a microcontroller or programmable logic device.Preferably, the accelerometer and electronic components of the systemfor embodiments of the invention comprise a solid state system with nomoving parts. Use of a solid state system with no moving parts allowsfreedom in design of the surrounding enclosures, leading to a potentialfor cost reductions in the unit since one unit can work with variablebrake sizes and geometries.

An accelerometer outputs, for example, current or voltage that isproportional to acceleration, which integrated over time equals speed ofan object, which in turn integrated over time results in distance.Accelerometers are available in many varieties including, for example,piezoelectric accelerometers, potentiometric accelerometers, andreductive accelerometers. Piezoelectric accelerometers use piezoelectriccrystals to produce an electric charge when a force is exerted underacceleration. Potentiometric accelerometers utilize displacement of aspring and mass linked to a wiper arm which moves across apotentiometer. Reductive accelerometers employ an inductance bridge toproduce an output voltage proportional to the movement of a mass bycausing the inductances of two coils to vary in opposing directions.

Other types of accelerometers include, for example, strain gaugeaccelerometers, capacitive accelerometers, and vibrating elementaccelerometers. Strain gauge accelerometers are piezoresistiveaccelerometers which use strain gauges acting as arms of a Wheatstonebridge to convert mechanical strain to DC voltage. In capacitiveaccelerometers, a change in acceleration causes a change in the spacebetween a moving and a fixed electrode. In vibrating elementaccelerometers, a small displacement of the mass varies the tension of atungsten wire in a permanent magnetic field and current through the wirecauses the wire to vibrate at a resonant frequency.

All accelerometers share the characteristic of measuring an accelerationin a given direction. Positive accelerometer readings are indicative ofan acceleration in the direction of orientation of the accelerometer.Negative accelerometer readings are indicative of an accelerationdirectly opposite or offset 180 degrees from the direction oforientation of the accelerometer. In a preferred embodiment of thepresent invention, the accelerometer comprises a device capable ofmeasuring an acceleration applied thereto.

A preferred embodiment of the present invention employs an accelerometersensor that comprises a surface micromachined polysilicon structurebuilt on top of the silicon wafer. Polysilicon springs suspend thestructure over the surface of the wafer and provide a resistance againstacceleration. Deflection of the structure is measured using adifferential capacitor that consists of independent fixed plates andcentral plates attached to the moving mass. The fixed plates are drivenby 180 degree-out-of-phase square waves. An acceleration deflects thebeam and unbalances the differential capacitor, resulting in an outputsquare wave whose amplitude is proportional to acceleration. Phasesensitive demodulation techniques are then used to rectify the signaland determine the direction of the acceleration.

In a preferred embodiment of the invention, the accelerometer comprisesa dual-axis accelerometer. Dual axis accelerometers have two sensors andmeasure acceleration along two axes. An alternate embodiment employs twounidirectional accelerometers, and acceleration is detected along twoaxes by mounting the two unidirectional accelerometers along differingaxes. Addition of the second axis of measurement is preferable, as thisgreatly simplifies the digital filtering required to reduce noise andvibrations. The output of the accelerometer x-axis and y-axis sensors isa direct current (DC) voltage that varies with measured acceleration.Thus, rotation of the brake cam shaft 26 is represented by a sine orcosine wave of DC voltage as output from the accelerometer.

In an embodiment of the invention, a dual axis accelerometer basedsensor 36 is attached to the brake cam shaft 26 in the location shown byFIG. 1, to measure the shaft rotation during brake actuation external tothe brake chamber 10. FIG. 3 is a schematic diagram that illustrates anexample of key components and flow of information between electroniccomponents for an embodiment of the invention. Referring to FIGS. 2 and3, a microcontroller 38 is used to translate the output signals of thedual axis accelerometer 36 into angular values representing the rotationof the brake cam shaft 26. By determining the rotation of the brake camshaft 26, the microcontroller 38 can calculate the brake stroke based onthe length of the slack adjuster 24 and can display the brake stroke ona display device 40 for a user.

In an embodiment of the invention, the dual axis accelerometer 36 ispositioned such that both axes are perpendicular to the brake cam shaftaxial centerline. Preferably, the two axes are offset from one anotherby 90 degrees, such that the axis of rotation of the cam shaft 26 andthe two axes of the accelerometer 36 are all perpendicular relative toeach other. By measuring the acceleration due to the earth's gravity ineach axis, a resultant vector can be calculated to determine a relativeposition for the brake cam shaft 26. By periodic sampling of the brakecam shaft position, a minimum and maximum angular value can bedetermined for a brake event. The difference between the minimum andmaximum angular values is the angular rotation experienced by the brakecam shaft 26. The push rod displacement, i.e., brake stroke, can then becalculated using the length from the axial center of the brake cam shaft26 to the axial center of the push rod linkage (effectively, the lengthof the slack adjuster 24).

FIG. 4 is a flow chart that illustrates an example of the process ofmeasuring a brake stroke of an air brake assembly for an embodiment ofthe invention. Referring to FIG. 4, at S1, an acceleration of a movablecomponent of the air brake assembly is detected during a braking eventby a sensor disposed external of a brake chamber of the air brakeassembly. At S2, the sensor generates an output signal that depends on amagnitude of the detected acceleration and sends the output signal to amicrocontroller. At S3, the microcontroller translates the sensor outputsignal to a value corresponding to a displacement of the movablecomponent of the brake assembly during the braking event, and at S4, themicrocontroller calculates a brake stroke distance based on said valueand sends the brake stroke information to a display device for a user.

FIG. 5 is a schematic diagram that illustrates an example of orthogonalaxes of a dual axis accelerometer in the gravitational field of theearth for an embodiment of the invention, and FIG. 6 is an outputvoltage diagram that shows an example of the x-axis output voltage andcorresponding y-axis output voltage in an acceleration event for anembodiment of the invention. Referring to FIGS. 2, 5 and 6, the x axis42 and y-axis 44 of the accelerometer 36 are disposed at right angles toone another and both are disposed at right angles to the axis 46 of thebrake cam shaft 26. The accelerometer 36 has a set of orthogonal axes,the x-axis 42 and the y-axis 44, that each give a voltage output 48, 50as illustrated in the example shown in FIG. 6. Placed in the earth'sgravitational field 52, the accelerometer 36 outputs an x-axis voltage48 and a y-axis voltage 50, or a voltage for each axis, which isproportional to the acceleration along the respective axis.

Referring further to FIGS. 2, 5 and 6, utilizing the x-axis voltageoutput 48 and the y-axis voltage output 50 with the inverse tangentfunction, θ₁=tan⁻¹ y₁/x₁, where y₁ and x₁ are the accelerometer y-axisoutput voltage 50 and x-axis output voltage 48, to get the angle ofrotation, θ₁, for the accelerometer 36. As previously noted, theaccelerometer 36 is affixed to the brake cam shaft 26 such that thebrake cam shaft axis 46 is orthogonal to both the x-axis 44 and they-axis 50 of the accelerometer 36.

FIG. 7 is a schematic diagram that illustrates an example of initial andfinal positions of the slack adjuster 24 and push rod 14 in a brakingevent for an embodiment of the invention. In the foregoing equation, θ₁represents an initial angular rotational position of the cam shaft 26.During a braking event, the brake cam shaft 26 rotates through a rangeof angles and then stops at a second position represented by θ₂ which isthe maximum angle attained by the cam shaft 26 relative to θ₁ during thebraking event. An embodiment of the invention yields a value for themaximum range of angular motion of rotation of the brake cam shaft.

Referring again to FIG. 7, during a braking event, the push rod 14extending from the brake chamber 10 pushes the slack adjuster 24 whichcauses the brake cam shaft 26 coupled to the S-cam 30 to rotate. Bymeasuring the angular rotation of the cam shaft 26 during a brakingevent, and with knowledge of a distance “S” between the axis 46 of thebrake cam shaft 26 and the pivot axis 54 of the push rod 14 coupled tothe slack adjuster 24, an embodiment of the invention yields a value “D”for the amount of displacement of the push rod 14.

Referring further to FIG. 7, at the second position of the slackadjuster 24, the angular rotation of the brake cam shaft 26 in thesecond position, θ₂, is likewise computed utilizing the inverse tangentfunction. The difference, Φ, between the rotational angle, θ₂, in thesecond position of the brake cam shaft 26 and the rotational angle, θ₁,in the first position of the brake cam shaft 26, represents the totalangle of rotation of the brake cam shaft 26 during a braking event.

As already mentioned, an embodiment of the invention utilizes theinverse tangent function to calculate initial and final angularrotations θ₁, θ₂, based on the x-axis and y-axis voltage outputs 48, 50of the accelerometer 36 for initial and final angular rotation positionsof the brake cam shaft 26 during a braking event. The difference φbetween θ₂ and θ₁ is then multiplied by the distance “S” between theaxis 46 of the brake cam shaft 26 and the pivot axis 54 of the push rod14 coupled to the slack adjuster 24 (i.e., the approximate length of theslack adjuster 24) to calculate the displacement “D” of the push rod 14during the braking event. While the actual calculated value “D”represents the arc length traveled by the pivot axis 54 of the push rod14 coupled to the slack adjuster 24, the difference between the chordlength and the arc length for such a small rotation is less thanone-half percent, which is more than adequately accurate for determiningthe displacement of the push rod 14, as a practical matter.

As also previously noted, the mounting alignment of the accelerometer 36for embodiments of the invention is not important, because therotational angles θ₁, θ₂ are measured relative to the acceleration ofgravity 52, such that orientation of the accelerometer 36 is notimportant, except that the x-axis 42 and y-axis 44 are orthogonal to theaxis 46 of the brake cam shaft 26. Further it is not necessary to mountthe accelerometer 36 along the axis 46 of the brake cam shaft 26, and itcan be simply strapped to the outside of the brake cam shaft 26 as longas the x-axis 42, the y-axis 44, and the axis 46 of the brake cam shaft26 are orthogonal to one another.

In an embodiment of the invention, the accelerometer 36 is incorporatedinto a sealed package that mounts directly to the brake cam shaft 26. Acable is employed to transmit the analog accelerometer output signals tothe microcontroller 38 for digitization of the values and calculation ofthe push rod displacement. In an alternate embodiment, the accelerometer36 can be mounted at locations other than the brake cam shaft 26. Forexample, the accelerometer 36 can be mounted to the push rod 14 or camroller 34. Additionally, in other embodiments of the invention, analogequivalents to the microcontroller 38 can be used to produce similarresults. A programmable logic device along with an analog to digitalconverter can also be used to achieve brake stroke length measurement.

In a further embodiment of the invention, the display device 40 ismounted proximate the vehicle wheel, preferably on or near the brakehousing and is coupled to the brake stroke sensor. In a preferredembodiment, the display device 40 can comprise, for example, a lightemitting diode (LED), liquid crystal display (LCD) or other suchlow-power display. In embodiments of the invention, the microcontroller38 operates the display device 40 to make brake stroke data visuallyavailable to a user. In a preferred embodiment, battery life is extendedby toggling the display such that it is only “on” when the vehicle isstationary.

In further embodiments of the present invention, a radio frequencyidentification (RFID) device, or other wireless communication device, isemployed to transmit accelerometer data from the brake region to aremote computer. Typically, such a system includes an interrogator atthe remote location that generates a modulated or unmodulated radiofrequency interrogation signal, and an RF “tag” incorporated into thebrake sensor to receive the signal from the interrogator and communicateaccelerometer data back to the interrogator.

The interrogator of the radio frequency (RF) communication system ispositioned proximate the brake system within range of the backscatter RFsignal. Such locations can include the passenger compartment of thevehicle on which the brake stroke sensor is mounted, a portablehand-held device positioned near the wheel, or associated with a storageor maintenance yard where such vehicles are kept. The interrogator mayfurther be associated with the display device 40 to provide brake strokesensor data to a user. In a preferred embodiment, the interrogator anddisplay device 40 are located within the passenger compartment of thevehicle to allow the driver to receive real time brake stroke data, andwarn of any dangerous conditions.

In a still further embodiment of the present invention, information fromthe brake stroke sensor is communicated from the wheel mounted locationto the interrogator and further to a wireless network such as a cellularor satellite network. In this embodiment, the interrogator is incommunication with a network interface that allows the information to befurther communicated throughout network. For example, a user at acentral monitoring station can monitor brake stroke sensor data for avehicle or fleet of vehicles simultaneously.

FIG. 8 is a schematic diagram that illustrates an example of deploymentof a plurality of brake stroke sensors in a vehicle brake system for anembodiment of the invention. Referring to FIG. 8, assume a vehicle, suchas a tractor or a trailer has, for example, four sets of dual wheels 60,62, 64, 66 for the drive axles or for the trailer load axles. In anembodiment of the invention, a brake stroke sensor 70, 72, 74, 76 isaffixed to each set of dual wheels 60, 62, 64, 66, and a microcontrollerand radio frequency (RF) transceiver or transmitter 78 serves as asingle collection point for the multiple sensors 70, 72, 74, 76 andreports the brake stroke information either to a remote device 80 ordisplays the data locally.

Thus, in an embodiment of the invention, an accelerometer 70, 72, 74, 76is associated with (e.g., mounted on) the brake cam shaft for each setof wheels 60, 62, 64, 66 and each is coupled via a cable or wirelesslyto an active or semi-passive RFID tag 78. Thus, the data from themultiple accelerometers 70, 72, 74, 76 comes into a single collectionpoint 78 and is transmitted from there via an RF link or infrared linkor some type of communication to a remote reader 80 or display orembedded device or PC.

Another aspect of the invention involves, for example, a gate reader setup such that one of the remote readers is a gate reader. In a furtheraspect of the invention, the same mobile communications platforms, suchas cellular, GLS, or satellite links that are currently in use, forexample, on tractor-trailer or bus tracking platforms that periodicallywirelessly report information on a truck in terms of location orinformation about the engine to a central location, can likewise by usedto communicate brake stroke information in the same type of system.

The embodiments of the present invention, described herein provide manyfeatures and advantages over the prior art systems and methods formeasuring brake stroke. These features and advantages include, forexample: a sensor that has no moving parts to break or wear out,installation of the device without alignment tools or brackets, thesensor automatically generates a zero or reference regardless of theinstalled position on the brake cam shaft, the sensor is sealed andimpervious to contaminants, and the system is electronic and thereforemay be digitized and transmitted elsewhere for data collection purposes.

Although the present invention has been described with reference toparticular embodiments, it should be recognized that these embodimentsare merely illustrative of the principles of the present invention.Those of ordinary skill in the art will appreciate that the apparatusand methods of the present invention may be constructed and implementedin other ways and embodiments. Accordingly, the description hereinshould not be read as limiting the present invention, as otherembodiments also fall within the scope of the present invention.

1. A system for measuring a brake stroke of an air brake assembly,comprising: a sensor mountable on a movable component of the air brakeassembly external of a brake chamber of the air brake assembly fordetecting an acceleration of the movable component during a brakingevent and for generating an output signal that depends on a magnitude ofthe detected acceleration; and a microcontroller coupled to the sensoron which is encoded program code consisting at least in part ofinstructions for translating the sensor output signal to a valuecorresponding to a displacement of the movable component of the brakeassembly during the braking event and for calculating a brake strokedistance based on said value.
 2. The system of claim 1, wherein thesensor further comprises an accelerometer for detecting acceleration ofthe movable component during the braking event.
 3. The system of claim1, wherein the sensor is adapted for detecting acceleration of themovable component along at least two different axes relative to themovable component during the braking event.
 4. The system of claim 3,wherein the sensor further comprises a dual axis accelerometer fordetecting acceleration of the movable component along the at least twodifferent axes relative to the movable component during the brakingevent.
 5. The system of claim 3, wherein the sensor further comprises atleast two unidirectional accelerometers for detecting acceleration ofthe movable component along the at least two different axes relative tothe movable component during the braking event.
 6. The system of claim1, wherein the output signal further comprises a direct current voltagethat varies in proportion to the magnitude of the detected acceleration.7. The system of claim 1, wherein the value corresponding to thedisplacement of the movable component further comprises angular valuesrepresenting a rotary displacement of the brake cam shaft during thebraking event.
 8. The system of claim 1, wherein the movable componentfurther comprises a push rod of the air brake assembly.
 9. The system ofclaim 1, wherein the movable component further comprises a cam roller ofthe air brake assembly.
 10. The system of claim 1, wherein themicrocontroller is coupled wirelessly to the sensor.
 11. The system ofclaim 1, further comprising a display device coupled to themicrocontroller for presenting brake stroke distance-related informationto a user.
 12. The system of claim 11, wherein the display devicefurther comprises a remote terminal coupled to the microcontroller. 13.The system of claim 11, wherein the display device is coupled wirelesslyto the microcontroller.
 14. The system of claim 11, wherein the displaydevice further comprises a portable hand-held display device coupledwirelessly to the microcontroller.